1. Field of the Invention
This invention relates to a selector valve used for stopping process flow and selecting its direction.
2. Related Art
A conventional selector valve which has heretofore been employed is illustrated in FIG. 5. This selector valve is composed of a cylindrical casing 1', a valve hood 4' covering the casing 1' at its top, a disk-shaped valve seat 2' fixedly secured to the inner bottom of the casing 1', a disk-shaped valve body 3' rotatable about its shaft and maintained in pressure contact with the valve seat 2' by means of a spring 6', several pairs of inlet and outlet ports 9', 10' each provided oppositely on the side periphery of the casing 1', and a passage 13' formed in the lower surface of the valve body 3' so as to be in fluid communication with selected one pair of the inlet and outlet ports 9', 10'.
Since the valve body 3' of the above selector valve rotates about its spool, it is difficult to balance pressure completely. Further, the spring, which urges the valve body, is often twisted between the valve body and the valve hood. Thus, the valve body can not rotate smoothly. In order to solve this problem, there is provided a selector valve in Japanese Published Unexamined Patent Application (Kokai) No. 61-252973. In this selector valve, air pressure is used instead of spring. However, the use of the air pressure causes fluid leakage and entry of compressed air into the process flow. Accordingly, the pressure of compressed air should be always adjusted so as to correspond with the pressure of the process flow.
Additionally, the above-mentioned conventional selector valves have a further problem because it is impossible to provide a large number of pairs of inlet and outlet ports on the side periphery of the casing. Moreover, since the outlet ports are subjected to various different fluid pressure, the pressure to be applied on the contact surface of the rotating valve body with the valve seat is required to be large enough. In order to obtain the large and adjustable pressure, several springs should be combined so as to define a multiple spring. However, in this condition, frictional force between the valve body and the valve seat is increased extremely, which adversely affects the rotation of the valve body.